As is known, the bar being machined in an automatic lathe, once inserted in the guiding channel of a feeder, is made to advance by means of a bar pusher toward the lathe, where it is picked up by the mandrel and turned to perform the machinings. The bar pusher is provided, at the front end, with a tool that consists of a fastening collet, which is composed of a plurality of jaws arranged in an annular configuration and allows to grip the rear end of the bar, push it toward the lathe to perform the machinings, and then recover and expel the unmachined end portion that remains in the collet when the bar pusher is retracted into the feeder.
Since the fastening collet has a larger diameter than the bar, it cannot pass through the devices provided to keep the bar guided at the output of the feeder and along the portion that leads from the output of the feeder to the mandrel of the lathe and are needed to eliminate or at least reduce the effects caused by geometric imperfections (eccentricities) and the polygonal cross-sections of the bars, and therefore harmful vibrations occur which affect the feeder and the lathe. In order to reduce these vibrations, it has already been suggested to arrange at the output of the channel of the feeder in which the bar is guided, a centering device that is composed of a ring of sectors that opens to allow the passage of the collet for fastening the bar pusher and closes when the collet has passed. For example, a device of this type is the subject of EP 1 669 145 in the name of this same Applicant.
However, known centering devices have proved to be complex in construction. Moreover, the elements that are intended to keep the bar centered do not rotate and therefore offer only support to the bar being machined, which instead rotates in them since it is turned by the lathe, and therefore wear of the jaws and vibrations occur.